1. Field of Invention
The present invention relates to a semiconductor structure and a method of forming the same, and more generally to a buried word line structure and a method of forming the same.
2. Description of Related Art
Non-volatile memories provide the property of multiple entries, retrievals and erasures of data, and are able to retain the stored information even when the electrical power is off. As a result, non-volatile memories are widely used in personal computers and consumer electronic products.
As the degree of integration of a non-volatile memory is getting higher, the critical dimension of the same is getting smaller. A buried word line structure is often employed in sub-28 nm memory technology or below to meet demands for scaling down the devices.
In order to effectively integrate active areas with isolation areas, for example, in a buried-WL DRAM structure, a portion of buried word lines can serve as active word lines for controlling the transistors in the cells, while another portion of buried word lines can serve as cell-to-cell isolation word lines. However, it has been difficult to effectively form such structure with the existing process steps.